Conventionally, there has been used a vacuum chuck as a general holding device for holding an object. However, when a thin plate is used as an object, the vacuum chuck is disadvantageous in that the periphery of the thin plate flexes. At the same time, according to an electrostatic holding device such as an electrostatic chuck, since an object can be held by the electrostatic force of the entire electrode plane, the periphery of the thin plate does not flex even when the thin plate is handled (held) (for example, reference to Japanese Patent Laid-Opens H7-257751, H9-322564. H10-66367, 2001-9766).
There have been known electrostatic holding devices illustrated in FIGS. 13, 15, and 17 as the above electrostatic holding device.
Here, in an electrostatic holding device (electrostatic chuck) of contact type 1100 shown in FIG. 13, a reference numeral 101 denotes a base member for attaching an electrode (electrostatic electrode) 103, and the electrode (electrode group) 103 including an electrode element 103a and an electrode element 103b, which is covered with an insulating material 102, is secured to the base member 101. In this case, a plurality of electrode elements 103a, 103b can be used respectively, and when a plurality of electrode elements 103a, 103b is used, electrode elements 103a, 103b are shown as an electrode element group 103a, 103b respectively.
These electrodes 103 are connected to a control portion (controller) 1105, which is connected to a switch SW. By means of ON/OFF operation of the switch SW, the control portion 1105 outputs a predetermined voltage (for example, +V1 to the electrode element 103a and −V1 to the electrode elements 103b) when the switch SW is turned on, and disconnects the voltage when the switch SW is turned off, as illustrated in FIG. 14. Therefore, when the switch SW is turned on, the electrostatic attraction is induced between the electrode (electrode surface) 103 and a handling object 104, and the handling object 104 is attracted to be held to a holding surface (attachment holding surface) 102a of the insulating material 102 by the electrostatic attraction. In addition, when the switch SW is turned off, the electrostatic attraction is removed. Accordingly, the electrostatic holding device 1100 functions as an electrostatic chuck by attracting the handling object 104 such as electric conductor, semiconductor, or high-resistance body with the electrostatic attraction or by eliminating the electrostatic attraction.
In an electrostatic holding device (electrostatic chuck) 1200 of floating type shown in FIG. 15, a surface (electrode surface 103) of an electrode 103 is covered with an insulating material 102, and the insulating material 102 is secured to a base plate 101. A displacement sensor 206 is provided to feedback a gap g (separation) between the electrode surface 103 and a handling object 104 such as electric conductor, semiconductor, or high-resistance body with an actual time.
The displacement sensor 206 passes through a through-hole 207 to measure the gap g between the handling object 104 and the electrode surface 103, and feedbacks the gap g to a controller 1205. The controller 1205 controls an applied voltage based on the measured gap g, and keeps the gap g in a previously set predetermined value. For instance, as illustrated in FIG. 16, when the gap g is larger than a target gap (gap>target), the controller applies predetermined direct-current voltage to induce the electrostatic attraction; thus the handling object 104 is attracted by the electrostatic attraction to reduce the gap g.
On the other hand, when the gap g is smaller than the target gap (gap<target), the controller disconnects the voltage to be applied to each of the electrodes (as 0V) to eliminate the attraction to the handling object 104; thus, the handling object 104 is lowered by the own weight to increase the gap g. The handling object 104 can be held to a predetermined gap g by repeating the above operations.
In an electrostatic holding device 1300 shown in FIG. 17, a pair of electrode element groups 503a, 503b is covered with an insulating member 102 which is secured to a base member 101. A control portion 1305 applies predetermine voltage to these electrode element groups 503a, 503b. Therefore, the electrostatic force is induced, and the handling object 104 is attracted to be held to the surface of the insulating material 102 (holding surface 102a) with the electrostatic attraction.